Hydrocarbon conversion catalysts

ABSTRACT

A catalyst, having a specified amount of rare earth metal content and a specified amount of alkali metal content, suitable for conversion of hydrocarbon oils to lower boiling products comprises a crystalline aluminosilicate zeolite, such as zeolite Y, an inorganic oxide matrix and, optionally discrete particles of alumina dispersed in the matrix. The zeolite prior to being composited with the matrix has a unit cell size above about 24.5 Angstroms. A cracking process utilizing the catalyst is also provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a catalyst and its use in a catalyticcracking process. More particularly, the present invention relates to acatalytic cracking catalyst having improved activity and selectivity forproducing high octane number naphtha.

2. Description of the Prior Art

Hydrocarbon conversion catalysts comprising a zeolite dispersed in asiliceous matrix are known. See, for example U.S. Pat. No. 3,140,249 andU.S. Pat. No. 3,352,796.

A catalyst comprising a zeolite, an inorganic oxide matrix and inertfines, which may be alpha alumina, is known. See U.S. Pat. No.3,312,615.

A catalyst comprising an amorphous silica-alumina, separately addedalumina and a zeolite is known. See U.S. Pat. No. 3,542,670.

A catalyst comprising a zeolite, an amorphous hydrous alumina andalumina monohydrate is known. See U.S. Pat. No. 3,428,550.

To improve the steam and thermal stability of zeolites, it is known toproduce zeolites having a low level of alkali metal content and a unitcell size less than about 24.45 Angstroms. See U.S. Pat. Nos. 3,293,192and Re. 28,629 (Reissue of U.S. Pat. No. 3,402,996).

It is also known to treat hydrogen or ammonium zeolite with H₂ O at atemperature ranging from about 800° to about 1500° F., and subsequentlycation exchanging the steam and water treated zeolite with cations whichmay be rare earth metal cations. The method increases the silica toalumina mole ratio of the zeolite. See U.S. Pat. No. 3,591.488.

U.S. Pat. No. 3,676,368 discloses a rare earth exchanged-hydrogenfaujasite containing from 6 to 14 percent rare earth oxides.

U.S. Pat. No. 3,957,623 discloses a rare earth exchanged zeolite havinga total of 1 to 10 weight percent rare earth metal oxide.

U.S. Pat. No. 3,607,043 discloses a process for preparing a zeolitehaving a rare earth content of 0.3 to 10 weight percent.

U.S. Pat. No. 4,036,739 discloses hydrothermally stable and ammoniastable Y zeolite in which a sodium Y zeolite is ion exchanged topartially exchange sodium ions for ammonium ions, followed by steamcalcination and a further ion exchange with ammonium to reduce the finalsodium oxide content to below 1 weight percent, followed by calcinationof the reexchanged product, or according to U.S. Pat. No. 3,781,199, thesecond calcination may be conducted after the zeolite is admixed with arefractory oxide.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided, a catalystcomprising:

(a) a crystalline aluminosilicate zeolite having uniform pore diametersranging from about 6 to about 15 Angstroms and a silica to alumina moleratio of at least about 3;

(b) an inorganic oxide matrix; and

(c) discrete particles of alumina;

said zeolite prior to being composited with (b) having a unit cell sizegreater than about 24.5 Angstroms, and said catalyst having an alkalimetal content such that the ratio of weight percent alkali metal,calculated as the alkali metal oxide, based on the total catalyst,divided by the weight percent zeolite based on the total catalyst is notgreater than 0.024 and a rare earth metal content such that the ratio ofweight percent rare earth metal, calculated as the rare earth metaloxide, based on the total catalyst, divided by the weight percentzeolite based on the total catalyst ranges from about 0.01 to about0.08.

In accordance with the invention there is further provided a catalyticcracking process utilizing the above stated catalyst.

DETAILED DESCRIPTION OF THE INVENTION

The catalyst of the present invention must have (1) an alkali metalcontent such that the ratio of weight percent alkali metal oxide basedon the total catalyst divided by the weight percent zeolite based on thetotal catalyst is not more than about 0.024, preferably not more thanabout 0.013 and (2) a rare earth content such that the ratio of weightpercent rare earth metal oxide based on the total catalyst divided bythe weight percent zeolite based on the total catalyst ranges from about0.01 to 0.08, preferably from about 0.01 to about 0.06, more preferablyfrom about 0.01 to about 0.04.

The alkali metal in the catalyst can be a single alkali metal or amixture of alkali metals. The rare earth metal may be a single rareearth metal or a mixture of rare earth metals of elements having atomicnumbers ranging from 57 to 71.

The required amount of rare earth metal and alkali metal can beincorporated into the catalyst either by preparing a zeolite having therequired rare earth content and alkali metal content and thencompositing the zeolite with a conventional matrix or the requiredamount of rare earth and alkali metal in the catalyst can be obtained byutilizing a zeolite having essentially no rare earth metal cations, thatis, less than 1 weight percent rare earth oxide based on the zeolite, orless than the required amount of rare earth metal and subsequentlytreating the composite catalyst (that is, zeolite dispersed in a matrix)with a solution comprising rare earth metal components to incorporatethe required amount of rare earth metal components into the catalyst.

The Zeolite Component

The initial zeolite component of the catalyst of the present inventionprior to being composited with the other components can be any of thelarge pore crystalline aluminosilicate zeolites having uniform poreopenings ranging from about 6 to about 15 Angstroms and a silica toalumina mole ratio of at least about 3. Examples of these zeolites arezeolites designated by the Linde Division of Union Carbide by the letterY (this zeolite has the structure of a faujasite and is described inU.S. Pat. No. 3,120,017) as well as naturally occurring faujasites. Thepreferred initial zeolite is a Y-type zeolite. The unit cell size of theinitial zeolite used prior to compositing it with the other componentsis greater than 24.5 Angstroms, preferably greater than about 24.6Angstroms.

The zeolite may comprise rare earth metal cations and may additionallycomprise hydrogen cations and cations of Group IB to VIII metals of thePeriodic Table of Elements. The Periodic Table referred to herein isgiven in Handbook of Chemistry and Physics, published by the ChemicalRubber Company, Cleveland, Ohio, 45th Edition, 1964. When additionalcations are present other than rare earth metals and alkali metals, thepreferred additional cations are calcium, magnesium, hydrogen andmixtures thereof. The concentration of hydrogen present in the finishedzeolite will be that concentration equivalent to the difference betweenthe theoretical cation concentration of the particular zeolite inquestion and the amount of cation present in the form of, for example,rare earth and residual ion.

When the rare earth content and low alkali metal of the catalyst arecontrolled by utilizing a zeolite which has been treated to comprise atleast a portion of the required rare earth metal, for example, as rareearth metal cations, the zeolite having the desired rare earth metalcomponent can be obtained by various methods.

One method of producing a required zeolite having only a limited amountof rare earth metal cations and low alkali metal content is to startwith a sodium Y-type zeolite having a unit cell size greater than 24.5Angstroms and ion exchange it with an ammonium ion by a conventionalmethod known in the art such as for example, by utilizing an ammoniumsalt in an aqueous or non-aqueous fluid medium. Ion exchange methods aredescribed, for example, in U.S. Pat. No. 3,140,249; U.S. Pat. No.3,140,251; U.S. Pat. No. 3,140,253, the teachings of which are herebyincorporated by reference. Although a wide variety of salts can beemployed, particular preference is given to chlorides, nitrates, andsulfate. The ion exchange treatment is conducted for a time sufficientto replace enough of the alkali metal cation by ammonium to decrease thealkali metal content of the zeolite to a desired value. The ammoniumtreatment may be a single treatment or a successive number oftreatments. If desired, the treated zeolite can be washed betweensuccessive ammonium treatments. The resulting ammonium exchanged zeoliteis recovered, for example, by filtration. The recovered zeolite iswashed with water to remove soluble matter. The ammonium exchanged Yzeolite is contacted with a fluid medium comprising rare earth metalcations of a single rare earth metal or cations of a mixture of rareearth metals. The ion exchange is conducted in a conventional way suchas by utilizing salts of the desired rare earth metals. The rare earthmetal treatment additionally replaces some of the remaining alkali metalcations of the zeolite and may replace some of the ammonium ions.

The amount of rare earth metal used is such that it does not exceed thelimits of the range required for the catalyst of the present invention.The total amount of required rare earth may be exchanged into thezeolite itself or only a portion of the amount required by the catalystof the present invention may be exchanged into the zeolite and thebalance of the desired required amount may be composited with thefinished catalyst, for example, by posttreating the finished catalystwith a solution comprising rare earth metal components that becomeassociated with the finished catalyst.

The rare earth-exchanged zeolite is recovered, for example, byfiltration, and washed with water to remove soluble matter and calcined,for example, at a temperature ranging from about 1300° F. to 1600° F.for about 0.5 to 6 hours, preferably from about 1400° F. to 1500° F. forabout 1 to 3 hours in the absence or in the presence of H₂ O which maybe steam or water.

The final zeolite may be composited with other catalytic metalcomponents, such as metals of Groups IIA, IIIA, IVA, IB, IIB, IIIB, IVB,VIB, and VIII of the Periodic Table of Elements.

The particle size of the zeolite component will generally range fromabout 0.1 to 10 microns, preferably from about 0.5 to 3 microns.Suitable amounts of the zeolite component in the total catalyst willrange from about 1 to 60, preferably from about 1 to 40, more preferablyfrom about 5 to 40, most preferably from about 8 to 35 weight percent,based on the total catalyst.

The Alumina Component

The catalyst of the present invention, optionally, comprises a porousalumina component. The porous alumina component is present in thepreferred catalyst of the present invention.

The porous alumina component of the catalyst of the present inventioncomprises discrete particles of various porous aluminas, preferablycrystalline alumina, which are known and commercially available. Ingeneral, the porous alumina component of the catalyst of the presentinvention are discrete particles having a total surface area, asmeasured by the method of Brunauer, Emmett and Teller (BET) greater thanabout 20 square meters per gram (m² /g), preferably greater than 145 m²/g, for example, from about 145 to 300 m² /g. Preferably the pore volume(BET) of the alumina will be greater than 0.35 cc/g. The averageparticle size of the alumina particles would generally be less than 10microns, preferably less than 3 microns. Preferably, the porous aluminawill be a material having initially, if used alone, prior to beingcomposited with the other components, inherently less catalytic crackingactivity of its own than the inorganic matrix component of the catalyst.Preferably, the porous alumina will be a bulk alumina. The term "bulk"with reference to the porous alumina is intended herein to designate amaterial which has been preformed and placed in a physical form suchthat its surface area and pore structure are stabilized so that when itis added to an impure, inorganic gel containing considerable amounts ofresidual soluble salts, the salts will not alter the surface and porecharacteristics measurably nor will they promote chemical attack on thepreformed porous alumina which could undergo change. For example,addition of "bulk" alumina will mean use of a material which has beenformed by suitable chemical reaction, the slurry aged, filtered, dried,washed free of residual salt and then heated to reduce its volatilecontent to less than about 15 weight percent. The porous aluminacomponent may suitably be present in the catalyst of the presentinvention in an amount ranging from about 5 to about 40 weight percent,preferably from about 10 to about 30 weight percent based on the totalcatalyst. Alternatively and optionally, an alumina hydrosol or hydrogelor hydrous alumina slurry may be used initially in the catalystpreparation as precursor of the discrete particles of alumina in thefinal catalyst.

The Inorganic Oxide Matrix Component

The inorganic oxide matrices suitable as component of the catalyst ofthe present invention are amorphous catalytic inorganic oxides, such assilica, alumina, silica-alumina, silica-zirconia, silica-magnesia,alumina-boria, alumina-titania and the like and mixtures thereof.Preferably, the inorganic oxide matrix is a silica-containing gel; morepreferably the inorganic oxide gel is an amorphous silica-aluminacomponent such as a conventional silica-alumina cracking catalyst,several types and compositions of which are commercially available.These materials are generally prepared as a cogel of silica and aluminaor as alumina precipitated on a preformed and preaged hydrogel. Ingeneral, the silica is present as a major component in the catalyticsolids present in said gels, being present in amounts ranging from about55 to 100 weight percent; preferably the silica will be present inamounts ranging from about 70 to about 90 weight percent. Particularlypreferred are two cogels, one comprising about 75 weight percent silicaand 25 weight percent alumina and the other comprising about 87 weightpercent silica and 13 weight percent alumina. The inorganic oxide matrixcomponent may suitably be present in the catalyst of the presentinvention in an amount ranging from about 40 to about 99 weight percent,preferably from about 50 to about 80 weight percent, based on the totalcatalyst. It is also within the scope of this invention to incorporatein the catalyst other materials, to be employed in cracking catalystssuch as various other types of zeolites, clays, carbon monoxideoxidation promoters, etc.

The catalyst of the present invention may be prepared by any one ofseveral methods. The preferred method of preparing one of the catalystsof the present invention, that is, a catalyst comprising silica-aluminaand porous alumina, is to react sodium silicate with a solution ofaluminum sulfate to form a silica/alumina hydrogel slurry which is thenaged to give the desired pore properties, filtered to remove aconsiderable amount of the extraneous and undesired sodium and sulfateions and then reslurried in water. Separately, the bulk alumina is made,for example, by reacting solutions of sodium aluminate and aluminumsulfate under suitable conditions, aging the slurry to give the desiredpore properties of the alumina, filtering, drying, reslurry in water toremove sodium and sulfate ions and drying to reduce volatile mattercontent to less than 15 weight percent. The alumina is then slurried inwater and blended in proper amounts, with a slurry of impuresilica-alumina hydrogel.

The zeolite component is added to this blend. A sufficient amount ofeach component is utilized to give the desired final composition. Theresulting mixture is then filtered to remove a portion of the remainingextraneous soluble salts therefrom. The filtered mixture is then driedto produce dried solids. The dried solids are subsequently reslurried inwater and washed substantially free of the undesired soluble salts. Thecatalyst is then dried to a residual water content of less than about 15weight percent. The catalyst is recovered after calcination for 6 hoursat 1000° F. in air. The catalyst of the present invention isparticularly suited for use in catalytic cracking of hydrocarbons.

Catalytic cracking with the catalyst of the present invention can beconducted in any conventional catalytic cracking manner. Suitablecatalytic cracking conditions include a temperature ranging from about700° F. to about 1300° F. and a pressure ranging from aboutsubatmospheric to several hundreds of atmospheres, typically from aboutatmospheric to about 100 psig. The process may be carried out in a fixedbed, moving bed, ebullating bed, slurry, transferline, or fluidized bedoperation. The catalyst of the present invention can be used to convertany of the conventional hydrocarbon feeds used in catalytic cracking,that is, it can be used to crack naphthas, gas oil and residual oilshaving a high content of metal contaminants. It is especially suited forcracking hydrocarbons boiling in the gas oil range, that is, hydrocarbonoils having an atmospheric pressure boiling point ranging from about450° to about 1100° F. to naphthas to yield not only products having alower boiling point than the initial feed but also products having animproved octane number.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following examples are presented to illustrate the invention.

Preparation of The Zeolite Component

A zeolite suitable as component of the catalyst of the present inventionwas made as follows:

(1) In a mixing tank, slurry 22 lbs of sodium Y zeolite in 100 lbs ofwater heated to 135° F.

(2) With stirring and continued heating, add 5 lbs of (NH₄)₂ SO₄.Continue to heat and stir at 135° F. for 2 hours, filter and rinse thefilter cake with 2 gallons of hot water. (A portion of the material wasanalyzed and showed 7.06 percent residual sodium oxide).

(3) In a mixing vessel, 100 lbs of water are heated to 135° F. and 5 lbsof ammonium sulfate dissolved in it. The pH of the solution was loweredto 4.0 by addition of sulfuric acid. With stirring and heating continuedat 135° F., the wet filter cake was added and contacted for 2 hours,filtered and rinsed with 2 gallons of hot water. A sample of thismaterial analyzed 4.60 weight percent sodium oxide.

(4) In a separate vessel charged 75 lbs of water, slurry the wet filtercake of (3) and heat the slurry to 135° F. With continued heating andstirring, add 850 cc of a solution of mixed rare earth chlorides(equivalent to 360 grams RE₂ O₃). Contact time was 1 hour. Filter andrinse with 3 gallons of hot water. A sample of this material analyzed4.48 weight percent sodium oxide and 5.37 weight percent RE₂ O₃.

(5) A portion of the filter cake was dried and calcined 6 hours at 1000°F. It had a unit cell size of 24.63 Angstroms and showed a crystallinityof 144 percent.

(6) The wet filter cake was placed in a furnace already at 1000° F. andthe temperature raised to 1500° F. maintaining 1500° F. for 30 minutesand then allowed to cool to 300° F. A portion of the material wasanalyzed. It had a unit cell size of 24.60 Angstroms and at acrystallinity of 141 percent. This material is suitable as a zeolitecomponent of the catalyst of the present invention.

EXAMPLE

Comparative cracking experiments were made utilizing catalysts A, B, C,D, E, F and G. Catalysts A, B, C and G are not catalysts in accordancewith the invention. Catalysts D, E and F are catalyst of the inventionwith catalysts D and E being preferred catalysts of the presentinvention. The compositions of the catalysts are shown in Table I.Catalysts A, B, C, D, E and F comprised about 20 weight percent of aY-type zeolite, about 20 weight percent of discrete particles of aporous alumina dispersed in about 60 weight percent silica-alumina gelmatrix. The Y-type zeolite in catalyst C was an ultrastable type Yzeolite. The same porous alumina and silica-alumina gel were used in thepreparation of catalysts A, B, C, D, E and F. Catalysts G was a standardcommercially available cracking catalyst comprising about 16 weightpercent rare earth metal exchanged Y-type zeolite, dispersed in a mixedmatrix of silica-alumina gel and kaolin. The rare earth metal content,calculated as rare earth metal oxide, based on total catalyst ofcatalyst G was about 3.74 weight percent. Catalyst A, which is not acatalyst of the present invention, was prepared by utilizing NaNH₄ Yzeolite which was neither rare earth exchanged nor calcined prior tobeing composited with the remaining catalyst components. Catalyst B,which is not a catalyst of the present invention, was prepared byutilizing a zeolite prepared from a sodium Y zeolite by direct exchangewith rare earth chlorides without a prior ammonium exchange. Catalyst C,which is not a catalyst of the present invention, was prepared from asodium Y zeolite by ammonium exchange followed by a 1500° F.calcination, followed by another ammonium ion exchange. The resultingzeolite was an ultrastable Y type zeolite. The zeolite of catalyst C wasnot subjected to rare earth exchange treatment.

Catalysts D, E and F, which are catalysts in accordance with the presentinvention, were each prepared by utilizing a sodium Y type zeolite whichwas subjected to ammonium exchange, followed by rare earth metal ionexchange and calcination at 1500° F. Catalysts A, B, C, D, E, and F werepost washed, that is, the composite catalysts were washed in the samemanner as is well known in the art, to remove residual salts.

Catalysts A, B, C, D, E, F and G were each steamed 16 hours at 1400° F.and 0 psig. The steamed catalysts were then evaluated for crackingactivity by a standard microactivity test (MAT). The results of thesetests are shown in Table II. The steamed catalysts were also evaluatedfor cracking performance in a full cycle cracking operation. The unitwas operated in a once-through manner, that is, there was no recycle oilmixed with fresh feed. The feedstock used was a 450° to 1100° F. vacuumgas oil. The unit was operated at a constant catalyst to oil ratio of 4.The reactor temperature was 925° F. and the regenerator temperature was1105° F. The catalysts were compared at a constant feed rate of 10 gramsper minute. The results are summarized in Table II.

As can be seen from the data in Table II, the octane number of thenaphtha product falls sharply when a catalyst is used in which the rareearth metal oxide content of the catalyst is 0.072 where the rare earthmetal content is calculated as the rare earth metal oxide of the totalcatalyst divided by the weight percent zeolite on total catalyst.

Catalyst G contained a fully rare earth exchanged Y type zeolite, thatis, all the exchangeable cationic positions were occupied by rare earthmetal cations. Catalysts D, E and F, which are catalysts in accordancewith the present invention, had a defined limited amount of rare earthmetal components in the total composite catalyst, and exhibited superioractivity.

                  TABLE I                                                         ______________________________________                                        Catalyst    A      B      C    D    E    F    G                               ______________________________________                                        Zeolite, wt. %                                                                            20     20     20   20   20   20   16                              Alumina, wt. %                                                                            20     20     20   20   20   20   --                              Silica-alumina,                                                               wt. %       60     60     60   60   60   60   60                              Kaolin, wt. %                                                                             --     --     --   --   --   --   20                              RE.sub.2 O.sub.3, wt. %.sup.(1)                                                           --     0.049   0   0.042                                                                              0.050                                                                              0.072                                                                              0.234                           Na.sub.2 O, wt. %.sup.(2)                                                                 0.041  0.024  0.010                                                                              0.008                                                                              0.012                                                                              0.010                                                                              0.038                           ______________________________________                                         .sup.(1) Rare earth metal oxide based on total catalyst divided by wt. %      zeolite on total catalyst.                                                    .sup.(2) Na.sub.2 O based on total catalyst divided by wt. % zeolite on       total catalyst.                                                          

                  TABLE II                                                        ______________________________________                                        Catalyst    A      B      C    D    E    F    G                               ______________________________________                                        Na.sub.2 O, wt. %.sup.(1)                                                                 0.041  0.024  0.010                                                                              0.008                                                                              0.012                                                                              0.010                                                                              0.038                           RE.sub.2 O.sub.3, wt. %.sup.(2)                                                           0      0.049  0    0.042                                                                              0.050                                                                              0.072                                                                              0.234                           MAT.sup.(3) 54.1   58.2   54.0 68.4 70.5 74.3 65                              Product Yield                                                                 Conversion.sup.(6)                                                            430° F. Conversion,                                                    vol. %      35.3   71.6   52.9 63.5 63.2 71.2 62.4                            C.sub.5 /430° F., vol. %                                                           33.9   61.8   47.7 59.3 59.0 65.0 58.4                            C.sub.3.sup.- dry gas, wt. %                                                              2.3    6.2    4.7  4.6  4.0  5.3  4.5                             C.sub.4.sup.=, vol. %                                                                     3.3    8.1    6.2  5.5  6.9  6.6  4.8                             iC.sub.4, vol. %                                                                          0.8    5.2    1.6  2.6  3.2  4.3  3.2                             Coke, wt. % 1.5    3.1    2.0  2.4  2.0  2.9  2.2                             C.sub.5 /430° F. Octanes                                               RONC.sup.(4)                                                                              91.7   92.1   93.0 92.6 92.2 90.6 89.9                            MONC.sup.(5)                                                                              --     80.3   79.9 80.2 79.3 79.3 78.6                             ##STR1##   --     86.2   86.4 86.4 85.7 84.9 84.2                            ______________________________________                                         .sup.(1) Na.sub.2 O based on total catalyst divided by wt. % zeolite on       total catalyst.                                                               .sup.(2) RE.sub.2 O.sub.3 based on total catalyst divided by wt. % zeolit     on total catalyst.                                                            .sup.(3) MAT is microactivity test. See Oil and Gas Journal, 1966, vol.       64, pages 7, 84, 85 and Nov. 2, 1971, pages 60-68.                            .sup.(4) Research Octane Number Clear.                                        .sup.(5) Motor Octane Number Clear.                                           .sup.(6) Conversion rate of 10 grams per minute.                         

What is claimed is:
 1. A catalyst comprising:(a) a crystallinealuminosilicate zeolite having uniform pore diameters ranging from about6 to about 15 Angstroms, and a silica to alumina mole ratio of at leastabout 3; (b) an inorganic oxide matrix, and (c) discrete particles ofalumina, said zeolite prior to being composited with (b) having a unitcell size greater than about 24.5 Angstroms, and said catalyst having analkali metal content such that the ratio of weight percent alkali metal,calculated as the alkali metal oxide, based on the total catalyst,divided by the weight percent zeolite based on the total catalyst is notgreater than 0.024 and a rare earth metal content such that the ratio ofweight percent rare earth metal, calculated as the rare earth metaloxide, based on the total catalyst, divided by the weight percentzeolite based on the total catalyst ranges from about 0.01 to about0.08.
 2. The catalyst of claim 1 wherein said alkali metal oxide ratiois not greater than about 0.013.
 3. The catalyst of claim 1 or claim 2wherein said rare earth metal oxide ratio ranges from about 0.01 toabout 0.06.
 4. The catalyst of claim 1 or claim 2 wherein said rareearth metal oxide ratio ranges from about 0.01 to about 0.04.
 5. Thecatalyst of claim 1 wherein said zeolite prior to being composited with(b) has a unit cell size greater than about 24.6 Angstroms.
 6. Thecatalyst of claim 1 wherein said zeolite is present in an amount rangingfrom about 1 to about 60 weight percent.
 7. The catalyst of claim 1wherein said zeolite is a Y-type zeolite.
 8. The catalyst of claim 1wherein said particles of alumina have a surface area greater than about20 m² /g and a pore volume greater than about 0.35 cc/g.
 9. The catalystof claim 1 wherein said particles of alumina in themselves have lesscracking activity than said inorganic oxide matrix.
 10. The catalyst ofclaim 1 wherein said particles of alumina are present in an amountranging from about 5 to about 40 weight percent, said zeolite is presentin an amount ranging from about 1 to about 40 weight percent and saidinorganic oxide matrix is present in an amount ranging from about 40 toabout 90 weight percent, each based on the total catalyst.
 11. Thecatalyst of claim 1 wherein said inorganic oxide matrix comprisessilica-alumina.